Class 12 Biology Chapter 16 Question Answers

Important Notes on 12 Biology Chapter 16

Pollution: Undesirable physical/chemical/biological characteristics of air/water/land which cause damage to the animals/plants/humans and architectural structures.

Reforestation: Process of restoring a forest that was removed at some point of time in the past.

Effluents: Something flowing over a large body of water (may be sewage or industrial effluents).

JFM (Joint Forest Management): Introduced by the Government of India in 1980s to work closely with local communities for protecting and managing forests.

Biomagnification

It refers to increase in concentration of toxic substances at successive trophic levels.

Harmful Effect of DDT: High concentration of DDT disturbs calcium metabolism in birds, which causes thinning of egg shell and their premature breaking, causing decline in birds population.

Global Warming: Increase in the level of greenhouse gases is mainly responsible for global warming, (increase in mean global temperature due to trapping of infrared radiation). Carbon dioxide, Methane, CFCs, N2O are the main gases that causes greenhouse effect.

Measures to Control Global Warming

Minimize the use of fossil fuel.

Improving efficiency of energy usage.

Reducing deforestation.

Planting trees.

Eutrophication: It is the process of nutrient enrichment of water and subsequent loss of species diversity like fishes. Excess nutrients causes algal bloom which may cover the whole surface of water body and release toxins. It causes oxygen deficiency in water that leads to the death of aquatic animals like fishes.

Ozone Hole: Large area of thinned ozone layer over Antarctica.

Steps leading to ozone depletion

UV-rays split CFCs and release atomic chlorine (Cl)

UV-rays also split ozone into oxygen.

Chlorine atoms trap oxygen atoms and ozone is not formed again from oxygen. This leads to depletion of ozone in the stratosphere.